125 - 
750 100 - X 
725 1 675 4 * 
mo} ~~ Tae 1 T_=360°C | 
5 oy ae = rea 5 em —a~3 =30 min 
625 . 
4 5 71] U 
89% 525 Me 
575- SCH 
550 Ws 
oe 
525 WO \ IM 
ne ee uma” aT wo * SN TNT NTT . 
150 ppp TTT TTT Vs rT TT 1 
o 0 a0 30 40 50 BO 70 BO 90 100 110 120 ' 10 20 30 40 60 60 70 80 90 100 1%0 120 . 
Distance from the wear surface, [um] Distance from the wear surface [um] I 
a) b) 
700 dl 
875 J 
650 
625 4 ' 
600 T,=350C Refer 
575 4 —8—1y 2 £0 min 
550 i 
525 (hb 
500 a 
475 (2) 
450 , or 
ne . ae 
A be 
YA SAN AI yer 1 
oc 10 20 30 4 60 60 70 80 80 100 110 120 . 
Distance from the wear surface [um] M 
c) 
Fig. 3. The variation of the microhardness function of the distance from the wear surface, for Tj, = 
350° C and some isothermal times Ti; : a) Ti; = 5 min; b) 7; = 30 min; ¢) 7; = 60 min. 
[GE 
Wear 
From the values presented in figure 2 and 3 it can be certainly observed a exponential evolution of 
the microhardness values. For all the five wear - test specimens, the microhardness (HV 0; ) 
decrease from the wear surface (2 um) to the interior of the section (120 um from the wear surface). Ad 
It ca be observed a general remarque that the microhardness decrease for the measurement who are (be 
made at 15 +35 um from the wear surface and then the microhardness present a constant value. um 
The maximum microhardness’s value was obtained for the specimen who are maintained at the 
isothermal level for 5 minutes. Less maintaining provides higher values for microhardness and this 
can be explained by the increasing of the proportion of the martensite, when the specimen are 
cooling in air after the isothermal maintaining. 
The wear surface’s hardened can be explained by the phase transformation in the surface near the 
wear process, zone where a part of the residual austenite are transformed in “s“martensite. 
The variation of the microhardness for a surface between 15 + 35 pm from the surface wear, are 
confirmed by Pearce (3) and Milosan (4). 
394